Conductive organic coatings

ABSTRACT

A conductive and weldable anti-corrosion composition for coating metal surfaces which contains:  
     (a) 5 to 40 wt. % of an organic binder containing:  
     (aa) at least one epoxide resin  
     (ab) at least one hardener selected from cyanoguanidine, benzoguanamine and plasticised urea resin  
     (ac) at least one amine adduct selected from polyoxyalkylenetriamine and epoxide resin/amine adducts  
     (b) 0 to 15 wt. % of an anti-corrosion pigment  
     (c) 40 to 70 wt. % of a conductive pigment selected from powdered zinc, aluminum, graphite, molybdenum sulfide, carbon black and iron phosphide  
     (d) 0 to 45 wt. % of a solvent;  
     and a lacquered metal structural part which has a conductive organic layer.

[0001] This invention relates to conductive and weldable anti-corrosioncompositions for coating metal surfaces and a process for coating metalsurfaces with electrically conductive organic coatings.

[0002] In the metal-processing industry, in particular when constructingvehicles, the metal constituents for the product have to be protectedagainst corrosion. According to the traditional prior art, the sheetmetal is first coated with anti-corrosion oils in the rolling mill andoptionally coated with drawing compounds prior to forming and punching.In the vehicle construction sector, appropriately shaped sheet metalparts are cut out for vehicle bodies or body parts and shaped using suchdrawing compounds or oils in a deep-drawing process, then they areassembled, generally by means of welding and/or flanging and/or bonding,and finally cleansed in a costly procedure. Anti-corrosion surfacetreatments, such as phosphatising and/or chromatising, then follow,whereupon a first lacquer layer is applied to the structural parts usingelectrodeposition. In general, this first electrodeposition process, inparticular in the case of car bodies, is followed by the application ofseveral more layers of lacquer.

[0003] In the metal processing industry, such as in the vehicle anddomestic appliance construction sectors, in order to simplify theprocess, there is a requirement to reduce the cost of chemicalanti-corrosion treatment. This may be achieved by providing the rawmaterial in the form of metal sheets or metal strips which have alreadybeen provided with an anti-corrosion layer.

[0004] There is, therefore, a need to find simpler methods of productionin which pre-coated sheets may be welded and then lacquered in anelectrodeposition process in the well-proven manner. Thus, there are anumber of processes in which, following phosphatising and/orchromatising in a so-called coil-coating process, an organic coating,which may conduct electricity to a greater or lesser extent, is applied.These organic coatings should as a rule be made up in such a way thatthey have sufficient electrical conductivity not to be impaired by thetypical welding processes used in the car industry, for exampleelectrical spot-welding. In addition, these coatings should beoverpaintable with conventional electrodeposition lacquers.

[0005] In particular in the car industry, in addition to normal steelsheeting, steel sheeting which has been galvanised and/or alloygalvanised in a variety of processes, has been used to an increasingextent recently.

[0006] The coating of steel sheeting with organic coatings which areweldable and which are applied directly in the rolling mill by theso-called coil-coating process is known in principle.

[0007] Thus, DE-C-3412234 describes a conductive and weldableanti-corrosion primer for electrolytically thin-layer galvanised,phosphatised or chromatised and drawable steel sheeting. Thisanti-corrosion primer consists of a mixture of more than 60% zinc,aluminum, graphite and/or molybdenum disulfide and also anotheranti-corrosion pigment and 33 to 35% of an organic binder and about 2%of a dispersion agent or catalyst. Polyester resins and/or epoxideresins and derivatives thereof are proposed as organic binders. It isassumed that this technology is the basis of the coating agent known inthe industry by the name “Bonazinc 2000”. Although this process providessome advantages as compared with the procedure described above(temporary corrosion protection with anti-corrosion oils followed bysubsequent degreasing after assembling the metallic components), theprocess described in DE-C-3412234 still requires much improvement:

[0008] The coating is not sufficiently spot-weldable.

[0009] Adhesion of the lacquer to the pretreated substrates, preferablygalvanised steels, is not always adequate, in particular when moresevere forming of the sheeting is performed in car presses.

[0010] In accordance with the disclosure in DE-C-3412234, the organicbinder may consist of polyester resins and/or epoxide resins andderivatives thereof. Specific examples mentioned are an epoxide/phenylprecondensate, an epoxy ester and linear oil-free mixed polyesters basedon terephthalic acid.

[0011] EP-A-573015 describes an organic-coated steel composite sheet,one or both surfaces of which are coated with zinc or a zinc alloy,which is provided with a chromate film and an organic coating appliedthereto which has a layer thickness of 0.1 to 5 μm. The organic coatingis formed from a primer composition which consists of an organicsolvent, an epoxide resin having a molecular weight between 500 and10,000, an aromatic polyamine and a phenol or cresol compound asaccelerator. Furthermore, the primer composition contains apolyisocyanate and colloidal silica. In accordance with the disclosurein this document, the organic coating is preferably applied so that thedry film layer thickness is 0.6 to 1.6 μm, since layers thinner than 0.1μm are too thin to provide corrosion protection. Layers thicker than 5μm, however, impair weldability. In an analogous manner, DE-A-3640662describes a surface-treated steel sheet consisting of a zinc-coated orzinc alloy-coated steel sheet, a chromate film produced on the surfaceof the steel sheet and a layer of a resin composition produced on thechromate film. This resin composition consists of a basic resin, whichis prepared by reacting an epoxide resin with amines, and apolyisocyanate compound. This film should also be used with a dry filmthickness of less than about 3.5 μm, because thicker layers greatlyreduce the weldability.

[0012] EP-A-380 024 describes organic coating materials based on abisphenolA- type epoxide resin having a molecular weight between 300 and100,000 and also a polyisocyanate or blocked polyisocyanate, pyrogenicsilica and at least one organic coloring pigment. A chromate-containingpretreatment with a high application of Cr is also required in thisprocess. The organic layer should be not thicker than 2 μm since sheetswith thicker organic layers do not enable satisfactory spot-welding andthere is a negative effect on the properties of the electrodepositionlacquer applied to the organic coating.

[0013] WO 99/24515 discloses a conductive and weldable anti-corrosioncomposition for coating metal surfaces, characterised in that itcontains:

[0014] (a) 10 to 40 wt. % of an organic binder containing:

[0015] (aa) at least one epoxide resin

[0016] (ab) at least one hardener selected from guanidine, substitutedguanidines, substituted ureas, cyclic tertiary amines and mixturesthereof

[0017] (ac) at least one blocked polyurethane resin

[0018] (b) 0 to 15 wt. % of an anti-corrosion pigment based on silicate

[0019] (c) 40 to 70 wt. % of powdered zinc, aluminium, graphite and/ormolybdenum sulfide, carbon black, iron phosphide

[0020] (d) 0 to 30 wt. % of a solvent.

[0021] There is a need to provide improved coating compositions whichsatisfy the requirements of the car industry in all respects. Incomparison to the prior art, the following properties of organic coatingcompositions suitable for the coil-coating process should be improved:

[0022] a clear reduction in white rust on galvanised steel sheeting inthe spray test according to DIN 50021, i.e. better corrosion protection,

[0023] an improvement in adhesion of the organic coating to the metallicsubstrate in accordance with an evaluation by the T-bend test (ECCAstandard) and impact test (ECCA standard),

[0024] ability to form an external skin (i.e. capacity for use asexternal sheet in a car body)

[0025] adequate corrosion protection, even with low rates of Cr,preferably also with Cr-free pretreatment processes,

[0026] the currently still conventional cavity sealing with wax orwax-containing products may become unnecessary due to the improvedcorrosion protection

[0027] adequate suitability for typical car welding processes.

[0028] The present invention provides a conductive and weldableanti-corrosion composition for coating metal surfaces, characterised inthat it contains, based on the total composition:

[0029] (a) 5 to 40 wt. % of an organic binder containing:

[0030] (aa) at least one epoxide resin

[0031] (ab) at least one hardener selected from cyanoguanidine,benzoguanamine and plasticised urea resin

[0032] (ac) at least one amine adduct selected frompolyoxyalkylenetriamine and epoxide resin/amine adducts

[0033] (b) 0 to 15 wt. % of an anti-corrosion pigment

[0034] (c) 40 to 70 wt. % of a conductive pigment selected from powderedzinc, aluminum, graphite, molybdenum sulfide, carbon black and ironphosphide

[0035] (d) 0 to 45 wt. % of a solvent,

[0036] and, if required, up to 50 wt. % of other active or auxiliarysubstances, wherein the proportions of the components total 100%.

[0037] A coating is to be understood to be electrically conductive, inthe context of the present invention, when it may be welded, aftercuring, under the conventional conditions for joint technology in thecar industry, in particular after a spot-welding process. Furthermore,these coatings have sufficient electrical conductivity to ensure thecomplete deposition of electrodeposition lacquers.

[0038] An essential constituent of the organic binder in theanti-corrosion composition according to the present invention is theepoxide resin. One epoxide resin or a mixture of several epoxide resinsmay be used. The epoxide resin(s) may have a molecular weight between300 and 100,000; epoxide resins having at least two epoxy groups permolecule which have a molecular weight of greater than 700 arepreferably used because, from experience, epoxides having highermolecular weights do not lead to occupational health and safety problemsduring application. Basically, a large number of epoxides may be used,such as the glycidyl ethers of bisphenol A or the glycidyl ethers ofNovolac resins. Examples of the former type are those sold by ShellChemie under the tradenames Epicote 1001, Epicote 1004, Epicote 1007,Epicote 1009. A number of other commercially available epoxide resins ofthe bisphenolA-/glycidyl ether type may also be used, as well as theepoxide resins mentioned above. Examples of Novolac epoxide resins arethe Araldit ECN products from Ciba Geigy, the DEN products from DowChemicals and also a number of other manufacturers.

[0039] Furthermore, epoxide group-containing polyesters may be used asepoxide resin binder components, these also including the epoxyderivatives of dimeric fatty acids.

[0040] These epoxide resins to be used according to the presentinvention are preferably solid, in the solvent-free state, at roomtemperature. When preparing the composition, they are used as a solutionin an organic solvent.

[0041] An epoxide based on bisphenol A glycidyl ether having a molecularweight of at least 800 is also preferred as an epoxide resin.

[0042] To harden the epoxide resin, the composition contains at leastone hardener selected from cyanoguanidine, benzoguanamine, plasticisedurea resin and mixtures thereof. The binder and hardener are preferablypresent in a ratio, by weight, of 0.8:1 to 7:1.

[0043] As another component, the organic binder also contains at leastone amine adduct selected from polyoxyalkylenetriamine and epoxideresin/amine adducts. Obviously, the binder may also contain a mixture ofseveral such adducts. The total amount of epoxide resin to the totalamount of amine adducts mentioned is preferably in the ratio, by weight,of 4:1 to 9:1, in particular 5:1 to 8:1.

[0044] As component (b), anti-corrosion pigments may be present in anamount of up to 15 wt. %. The composition preferably contains 2 to 10wt. % of anti-corrosion pigment, selected from doped silicas, silicatesof divalent metals, in particular calcium-containing modified silicates,aluminum and zinc phosphates and modification products thereof andsurface-modified titanium dioxide.

[0045] The agent contains, as conductive pigment (c), a powder of anelectrically conductive substance which enables the coated metalsurfaces to be electrically welded and electrophoretically lacquered,for example by cathodic electrodeposition lacquering. The electricallyconductive substance is preferably selected from zinc, aluminum,graphite, carbon black, molybdenum sulfide and/or iron phosphide, eachbeing in the powdered form. Powdered iron phosphide is preferably usedand this preferably has an average particle size of not more than 10 μm.This type of powder may be obtained by milling a more coarsely dividedpowder. The average particle size is preferably in the range 2 to 8 μm.Known methods, such as light scattering or electron microscopy, areavailable for determining particle sizes.

[0046] The anti-corrosion composition also contains 0 to 30 wt. % of asolvent or a solvent mixture, wherein some of this solvent or solventmixture may be incorporated by means of the epoxide resin component orother components of the binder. This applies in particular whencommercially available binder components are used in the agent. Suitablesolvents are solvents based on ketones which are normally used inlacquer technology, such as methyl ethyl ketone, methyl isobutyl ketone,methyl n-amyl ketone, ethyl amyl ketone, acetylacetone, diacetonealcohol and also γ-butyro-lactam and N-alkylated products thereof whichcontain alkyl groups having 1 to 3 carbon atoms. Furthermore, aromatichydrocarbons, such as toluene, xylene or mixtures thereof, may be used,and also aliphatic hydrocarbon mixtures having boiling points betweenabout 80 and 180° C. Other suitable solvents are, for example, esters,such as ethyl acetate, n-butyl acetate, isobutyl isobutyrate, oralkoxyalkyl acetates, such as methoxypropyl acetate or 2-ethoxyethylacetate. Furthermore, monofunctional alcohols such as isopropyl alcohol,n-butanol, methylisobutylcarbinol or 2-ethoxyethanol or monoalkyl ethersof ethylene glycol, diethylene glycol or propylene glycol may bementioned as representative of many suitable solvents. It may beexpedient to use mixtures of the previously mentioned solvents.

[0047] In particular, solvent (d) may be selected from diacetonealcohol, butyldiglycol acetate, aromatic compound-rich hydrocarbons,xylene, 3-methoxybutyl acetate, methoxyacetoxypropane, benzyl alcohol orbutanol.

[0048] The composition may contain, as optional other active orauxiliary substances, one or more substances selected from modifiedcastor oil, modified polyethylene wax and polyethersiloxane copolymers.

[0049] One particular advantage of the composition according to thepresent invention is that the organic binder component may contain noisocyanates. This means that the health risks associated with the use ofisocyanates are avoided.

[0050] The agent according to the present invention is particularlysuitable for use in the so-called coil-coating process. Here, metalstrips are continuously coated. The agent may be applied by a variety ofmethods which are commonplace in the prior art. For example, applicationrollers may be used which may be adjusted directly to give the desiredwet film thickness. Alternatively, the metal strip may be dipped in theagent or it may be sprayed with the agent.

[0051] Provided metal strips which have been coated immediatelybeforehand, in an electrolytic or melt-dip process, with a layer ofmetal, for example with zinc or zinc alloys, are coated, then cleansingof the metal surfaces prior to applying the agent is not required.However, if the metal strips have been stored for a time and inparticular if they have been treated with anti-corrosion oils, then acleansing step is required. The agent according to the present inventionmay be applied directly to the cleansed or polished, depending on themethod of manufacture, metal surface. The anti-corrosion effect whichmay be produced may be improved, however, if the metal surface issubjected to an anti-corrosion pretreatment using inorganic reagentsprior to applying the agent, using the technique known in the prior artas “conversion treatment”. This may be, for example, a phosphatisingprocess, in particular layer-forming zinc phosphatising, a chromatisingprocess or a conversion treatment using chromium-free treatment agents,for example one based on the complex fluorides of titanium and/orzirconium. These types of pretreatment processes are known from theprior art. If a chromatising process is selected as a pretreatment, thisis preferably performed in such a way that a chromium application of notmore than 30 mg per m², for example 20 to 30 mg of chromium per m², isobtained. Higher rates of application of chromium are not required.

[0052] The agent according to the present invention is preferablyapplied to the metal surface at a wet film thickness such that, aftercuring, the resulting layer has a thickness of about 1 to about 10 μm.Layers having thicknesses in the range of about 8 μm, for example 5 to 9μm, are preferably produced. The organic coating is cured by heating thecoated metal surface to an object temperature (PMT=peak metaltemperature) in the range 160 to 260° C. The preferred PMT is in therange 230 to 260° C.

[0053] To cure the coating on the substrate, the coated substrate isheated until the temperature has risen to a value within the rangementioned. This heating procedure may take place, for example, in aheated furnace, in particular in a continuous furnace, which mustgenerally have a temperature well above the PMT and is preferablyoperated with circulating air. The furnace temperature may be, forexample, 350° C., wherein the PMT may be controlled via the residencetime of the coated substrate in the furnace zone. The procedure ispreferably such that the substrate is not held at the PMT for anextended period, but is allowed to cool down immediately after reachingthe PMT. Active cooling measures, such as cooling with water or blowingwith air may be provided for this purpose. The time up to reaching thePMT may be less than one minute, for example about 30 seconds, whenapplied as a coil-coating process.

[0054] Accordingly, in another embodiment, the present invention alsoprovides a process for coating metal surfaces with a conductive organicanti-corrosion layer characterised by the following steps:

[0055] (i) a conventional pretreatment consisting of:

[0056] cleansing

[0057] phosphatising, if required

[0058] chromatising, if required

[0059] chromium-free pretreatment, if required

[0060] (ii) coating with a composition as claimed in any one of claims 1to 7, in a layer thickness of 1 to 10 μm, preferably between 5 and 9 μm

[0061] (iii) curing the organic coating at temperatures between 160 and260° C. peak metal temperature (PMT).

[0062] The metal surfaces to be coated are preferably selected fromsurfaces of steel which have been galvanised or alloy galvanised,electrolytically or in a hot dip process, or of aluminum. Examples ofalloy galvanised steels are the materials Galvannealed® (Zn/Fe alloy),Galfan® (Zn/Al alloy) and Zn/Ni alloy coated steel.

[0063] Furthermore, the present invention relates to a metal objecthaving an anti-corrosion layer which is obtainable by the processaccording to the present invention. The anti-corrosion layer producedaccording to the present invention may also be overpainted with furtherlayers of lacquer.

[0064] When using metal parts coated according to the present invention,for example in the vehicle construction sector and in the domesticappliance industry, chemical treatment stages for the anti-corrosiontreatment of the final structural parts are not required. The assembledstructural parts which have a coating according to the present inventionmay be directly overpainted, for example by powder coating or byelectrolytic dip lacquering. In places where overpainting cannot takeplace, for example in cavities in vehicle bodies, metal parts coatedaccording to the present invention have an adequately high resistance tocorrosion. Costly working procedures, such as cavity conservation arenot required here. This simplifies the finishing processes involved invehicle construction and this also leads to a saving in weight comparedwith conventional cavity sealing processes, and thus to a lower fuelconsumption.

[0065] One advantage of a material coated according to the presentinvention is the fact that it may be used as an ‘external skin’ whenconstructing a vehicle. The number of welding points per electrode whichmay be achieved during resistance spot welding is higher than for theprior art coatings cited above. When applied to the materialGalvannealed®, which is known to be brittle and difficult to thermoformby pressing, it exhibits very good pressing behavior, so that lessabrasion is produced during pressing. Furthermore, the ‘cratering’(defects in the lacquer) which is known to occur during cathodicelectrodeposition lacquering of Galvannealed® is prevented.

[0066] The conductive organic layer produced by the present process thusprovides a base for further overpainting, as is generally conventionalin the metal construction industry. A powder coating layer, for example,may be applied to the conductive organic layer. Thus, the presentinvention, in an extended embodiment, relates to a metal object whichhas a coating system on the metal surface consisting of the followingindividual layers:

[0067] (a) a chemical conversion layer,

[0068] (b) a conductive organic layer having a thickness of 1 to 10 μm,containing at least an organic binder and an electrically conductivesubstance,

[0069] (c) a powder coating layer having a thickness of 70 to 120 μm.

[0070] A powder coating is conventionally used in particular for machineconstruction, metal parts for the internal structure of buildings and inthe furniture and domestic appliance industry. In the vehicleconstruction sector, due to the higher degree of mechanical andcorrosive strain, a multi-layered system in which a differentiatedsequence of organic coatings is applied on top of a chemical conversionlayer is currently preferred. In this sequence, a conductive organiclayer follows on top of the conversion layer, as the first organiclayer. Then, a simplified layer structure, as compared to that used inthe prior art, may follow consisting of an electrodeposition lacquer andone or two layers of top-coat. Since the underlying material has alreadybeen provided with the conductive organic layer, the steps required bythe vehicle manufacturer to produce a chemical conversion layer and toapply the various organic coatings are simplified.

[0071] The present invention thus also includes a metal object whichhas, on the metal surface, a coating system consisting of the followingindividual layers:

[0072] (a) a chemical conversion layer,

[0073] (b) a conductive organic layer having a thickness of 1 to 10 μm,containing at least an organic binder and an electrically conductivesubstance,

[0074] (c) an electrodeposition lacquer having a thickness of 25 to 35μm

[0075] (d) one or two layers of topcoat.

[0076] Hitherto, it has not been conventional in the prior art to applyan electrodeposition lacquer onto an organic layer. According to thepresent invention, an electrodeposition lacquer having a thickness inthe range 25 to 35 μm may be applied to the conductive organic layer.This is a much thicker layer than is conventional in the prior art,where an electrodeposition lacquer having a thickness of about 20 μm isdeposited directly onto a chemical conversion layer. In the prior art,as described hitherto, a filler follows the electrodeposition lacquerand only then are one or two layers of topcoat applied. In accordancewith the present invention, the filler layer may be dispensed with sinceits function (in particular increasing the resistance to impact bystones) is taken over by the electrodeposition lacquer. Therefore, onelacquering step is saved. In addition, the entire coating system inaccordance with the present invention is thinner than is conventional inthe prior art. This means that materials are saved, which leads toeconomic and ecological advantages.

[0077] The topcoat may be specified as a single layer or two layers. Inthe two-layered specification, it consists of a so-called basecoat,which primarily provides optical effects in the coating system, and aclear coat which has a substantially protective function and throughwhich the basecoat is visible.

[0078] In the two previously described cases, the chemical conversionlayer may be a coating which is produced by a conversion treatment asdescribed further above, for example by a phosphatising or chromatisingprocess or a conversion treatment using chromium-free treatment agents.The conductive organic layer (b) provided may be a layer which isobtainable by the previously described process according to the presentinvention. Another process for applying a conductive organic layer isknown from DE 199 51 133, which is not a prior publication. The layerdescribed there has the advantage of curing at a temperature (PMT) inthe range 130 to 159° C. Therefore it may also be used for so-calledbake-hardening steels. With regard to this, the present inventionrelates to a metal object of the previously described type, in which theconductive organic layer (b) is obtained by applying a coating agenthaving the composition:

[0079] (i) 10 to 30 wt. % of an organic binder which cures at atemperature of 140 to 159° C., preferably between 149 and 159° C.,

[0080] (ii) 30 to 60 wt. % of a powder of an electrically conductivesubstance,

[0081] (iii) 10 to 40 wt. % of water and

[0082] (iv) if required, a total of up to 30 wt. % of other activeand/or auxiliary substances, wherein the amounts total 100 wt. %, to themetal surface provided with chemical conversion layer (a) and cured at apeak metal temperature in the range 130 to 159° C.

[0083] The present invention also includes the processes for coating ametal object which lead to the previously described metal objects. Thisprovides a process for coating a metal object, characterised in that thefollowing layers are applied in sequence to at least part of the surfaceof the metal object:

[0084] (a) a chemical conversion layer,

[0085] (b) a conductive organic layer having a thickness of 1 to 10 μm,containing at least an organic binder and an electrically conductivesubstance,

[0086] (c) an electrodeposition lacquer having a thickness of 25 to 35μm,

[0087] (d) a powder coating having a thickness of 70 to 120 μm.

[0088] Furthermore, this provides a process for coating a metal object,characterised in that the following layers are applied in sequence to atleast part of the surface of the metal object:

[0089] (a) a chemical conversion layer,

[0090] (b) a conductive organic layer having a thickness of 1 to 10 μm,containing at least an organic binder and an electrically conductivesubstance,

[0091] (c) an electrodeposition lacquer having a thickness of 25 to 35μm,

[0092] (d) one or two layers of topcoat.

[0093] Reference is made here to the previous explanations relating tothe individual layers (a) to (d).

EXAMPLES

[0094] The following Tables give examples of compositions. Sample sheetsof electrolytically galvanised steel, which are coated with aconventional industrial chromatising layer and on which the conductiveorganic coating is cured at a PMT of 235-250° C. to give a layer havinga thickness in the range 5 to 9 μm, produced the following results inconventionally used application tests: solvent resistance according tothe methyl ethyl ketone test, as described in DIN 53339: more than 10double wipes; corrosion effects after 10 cycles in a variable climatetest in accordance with VDA 621-415: red rust on the flange: r0, lacquercreep corrosion at a scratch (half scratch width)<1.5 mm. TABLE 1Example compositions (in wt. %) Example no./Component 1 2 3 4 5Toluylene diisocyanate Cyanoguanidine 2.3 1.6 2.6 2.7 Butyl diglycol(from binder) 1.5 0.7 0.7 1.6 1.7 Hexamethylene diisocyanate Plasticisedurea resin 1.5 Doped silica 4.1 5.0 4.5 4.1 4.8 Glycol ether (Dowanol ®PMA) 14.0 6.6 Glycol ether (Dowanol ® PM) 5.3 15.2Polyalkoxyalkylenetriamine Polyethersioxane copolymer Bisphenol A resin7.0 5.5 5.0 7.7 8.2 Zinc dust 5.0 N-methylation product of 3.1 3.1 3.5γ-butyrolactam Benzoguanamine 1.3 Isophorone diisocyanate 2.0Diphenylmethane diisocyanate 2.5 2.0 Diacetone alcohol 8.8 9.0 9.6 10.2Butyldiglycol acetate 15.5 17.0 10.0 9.3 4.8 Aromatic-rich hydrocarbon2.3 2.0 6.6 2.7 (Solvesso ® 200) Xylene 1.3 0.6 3-methoxybutyl acetateDispersion aid 0.4 Modified PE wax 0.4 0.2 Iron phosphide 45.3 45.0 47.041.4 52.6 Benzyl alcohol 4.8 Butanol 1.5 0.7 0.7 1.6 1.7 Epoxy-modifiedamine adduct 1.6 1.3 1.6 1.9 Modified castor oil 0.2 Aluminum 4.0Molybdenum sulfide Surface-modified Ti oxide Total solids 60.7 65.8 63.661.6 70.6 Total pigment content 49.4 55.0 51.5 49.5 57.4 Total bindercontent 11.3 10.8 12.1 12.1 13.2 Example no./Component 6 7 8 9 10Toluylene diisocyanate 3.0 Cyanoguamdine 2.7 2.2 2.3 Butyl diglycol(from binder) 1.7 1.3 0.7 0.5 1.5 Hexamethylene diisocyanate Plasticisedurea resin Doped silica 4.8 5.0 7.0 5.0 4.1 Glycol ether (Dowanol ® PMA)Glycol ether (Dowanol ® PM) 15.2 11.0 Polyalkoxyalkylenetriainine 2.55.0 Polyethersiloxane copolymer Bisphenol A resin 8.2 6.5 5.5 5.3 7.0Zinc dust 8.7 N-methylation product of 9.5 3.1 γ-butyrolactamBenzoguanamine 1.3 Isophorone diisocyanate Diphenylinethane diisocyanate2.5 Diacetone alcohol 10.2 8.0 5.0 8.8 Butyldiglycol acetate 7.9 22.0Aromatic-rich hydrocarbon 2.7 2.2 2.3 (Solvesso ® 200) Xylene 1.1 0.63-methoxybutyl acetate 11.0 10.7 Dispersion aid 0.8 Modified PB wax 0.40.2 Iron phosphide 52.6 45.0 43.0 42.3 45.3 Benzyl alcohol 5.0 15.0 13.3Butanol 1.7 1.3 0.7 0.5 1.5 Epoxy-modified amine adduct 2.5 1.3 1.6Modified castor oil 0.4 Aluminum Molybdenum sulfide Surface-modified Tioxide Total solids 70.8 61.6 60.8 69.7 61.1 Total pigment content 57.450.0 50.0 56.0 49.4 Total binder content 13.4 11.6 10.8 13.7 11.7Example no./Component 11 12 13 14 15 Toluylene diisocyanateCyanoguanidine 2.3 2.7 2.2 2.4 Butyl diglycol (from binder) 1.5 0.5 1.71.4 1.5 Hexainethylene diisocyanate 5.0 Plasticised urea resin Dopedsilica 4.1 5.0 4.8 3.8 3.0 Glycol ether (Dowanol ® PMA) 4.4 Glycol ether(Dowanol ® PM) Polyalkoxyalkylenetriamine 5.0 0.5 Polyethersiloxanecopolymer 0.1 Bisphenol A resin 7.0 5.3 8.2 6.5 7.2 Zinc dust 6.8N-methylation product of 3.1 3.4 2.8 14.1 γ-butyrolactam BenzoguanamineIsophorone dusocyanate Diphenylmethane diisocyanate Diacetone alcohol8.8 5.0 10.2 8.0 9.0 Butyldiglycol acetate 11.2 5.0 22.4 Aromatic-richhydrocarbon 2.3 2.7 3.0 2.4 (Solvesso ® 200) Xylene 0.6 0.63-methoxybutyl acetate 18.3 Dispersion aid 0.1 Modified PE wax 0.2 0.2Iron phosphide 38.5 41.7 52.6 41.8 45.0 Benzyl alcohol 11.1 13.3 5.0 9.0Butanol 1.5 0.5 1.7 1.4 1.5 Epoxy-modified amine adduct 1.6 1.4 1.5 1.8Modified castor oil 0.1 0.4 0.3 Aluminum Molybdenum sulfideSurface-modified Ti oxide 2.0 Total solids 60.5 62.4 70.2 56.0 61.9Total pigment content 49.4 46.7 57.4 45.6 50.0 Total binder content 11.115.7 12.8 10.4 11.9 Example no./Component 16 17 18 19 20 Toluylenediisocyanate 5.0 Cyanoguanidine 2.2 2.3 1.6 2.2 Butyl diglycol (frombinder) 1.4 0.5 1.5 0.7 1.4 Hexamethylene diisocyanate Plasticised urearesin 2.0 1.5 Doped silica 5.0 5.0 5.0 4.5 5.0 Glycol ether (Dowanol ®PMA) 4.0 15.0 14.7 4.0 Glycol ether (Dowanol ® PM) 5.5 9.0Polyalkoxyalkylenetriamine Polyethersiloxane copolymer 0.1 0.1 BisphenolA resin 6.5 6.3 7.0 5.0 6.5 Zinc dust N-methylation product of 2.8 22.52.9 γ-butyrolactam Benzoguanamine Isophorone diisocyanate 2.0Diphenylmethane diisocyanate 2.0 Diacetone alcohol 8.0 5.2 8.7 5.3 8.0Butyldiglycol acetate 17.4 4.8 10.0 17.8 Aromatic-rich hydrocarbon 2.82.4 2.0 2.8 (Solvesso ® 200) Xylene 1.1 1.8 1.1 3-methoxybutyl acetateDispersion aid 0.4 0.2 Modified PE wax 0.4 0.6 0.4 Iron phosphide 45.050.0 45.0 38.0 45.0 Benzyl alcohol Butanol 1.4 0.5 1.5 0.7 1.4Epoxy-modified amine adduct 1.5 1.6 1.5 Modified castor oil AluminumMolybdenum sulfide 3.0 Surface-modified Ti oxide Total solids 61.0 68.561.6 57.6 60.6 Total pigment content 50.0 55.0 50.0 45.5 50.0 Totalbinder content 11.0 13.5 11.6 12.1 10.6 Example no./Component 21 22 2324 25 Toluylene diisocyanate Cyanoguamdine 2.3 2.7 2.3 2.7 Butyldiglycol (from binder) 1.5 1.7 0.5 1.5 1.7 Hexamethylene diisocyanate3.0 Plasticised urea resin Doped silica 4.1 4.8 5.0 5.0 4.8 Glycol ether(Dowanol ® PMA) Glycol ether (Dowanol ® PM) Polyalkoxyalkylenetriainine5.0 2.5 Polyethersiloxane copolymer 0.1 Bisphenol A resin 7.0 8.2 5.37.0 8.2 Zinc dust 8.7 N-methylation product of 3.1 3.7 24.3 1.6γ-butyrolactam Benzoguanamine Isophorone diisocyanate Diphenylmethanediisocyanate Diacetone alcohol 8.8 10.2 5.0 8.7 10.2 Butyldiglycolacetate 11.2 5.0 5.4 Aromatic-rich hydrocarbon 2.3 2.7 2.4 2.7(Solvesso ® 200) Xylene 3-methoxybutyl acetate 11.0 Dispersion aid 0.10.6 Modified PE wax Iron phosphide 45.3 52.6 42.3 45.0 52.6 Benzylalcohol 11.1 5.0 13.3 5.0 Butanol 1.5 1.7 0.5 1.5 1.7 Epoxy-modifiedamine adduct 1.6 1.7 1.6 0.9 Modified castor oil 0.1 0.4 AluminumMolybdenum sulfide Surface-modified Ti oxide Total solids 60.5 70.0 69.761.6 71.7 Total pigment content 49.4 57.4 56.0 50.0 57.4 Total bindercontent 11.1 12.6 13.7 11.6 4.3 Example no./Component 26 27 28 Toluylenediisocyanate 2.7 Cyanoguanidine 2.2 2.2 Butyl diglycol (from binder) 1.31.3 0.5 Hexamethylene diisocyanate 2.7 Plasticised urea resin Dopedsilica 2.5 5.0 4.0 Glycol ether (Dowanol ® PMA) Glycol ether (Dowanol ®PM) Polyalkoxyalkylenetriamine 4.1 Polyethersiloxane copolymer BisphenolA resin 6.5 6.5 5.3 Zinc dust N-methylation product of 9.5 14.8γ-butyrolactam Benzoguanamine Isophorone diisocyanate Diphenylmethanediisocyanate 2.7 Diacetone alcohol 8.0 8.0 5.0 Butyldiglycol acetateAromatic-rich hydrocarbon 2.2 2.2 (Solvesso ® 200) Xylene 1.1 0.63-methoxybutyl acetate 10.0 Dispersion aid Modified PE wax 0.4 0.2 Ironphosphide 45.0 45.0 48.8 Benzyl alcohol 15.0 10.0 13.3 Butanol 1.3 1.30.5 Epoxy-modified amine adduct 2.5 2.5 Modified castor oil 0.4 0.4Aluminum Molybdenum sulfide Surface-modified Ti oxide 2.5 Total solids61.6 61.8 68.7 Total pigment content 50.0 50.0 53.5 Total binder content11.6 11.8 15.2

1. A conductive and weldable anti-corrosion composition for coatingmetal surfaces, characterised in that it contains, based on the totalcomposition: (a) 5 to 40 wt. % of an organic binder containing: (aa) atleast one epoxide resin (ab) at least one hardener selected fromcyanoguanidine, benzoguanamine and plasticised urea resin (ac) at leastone amine adduct selected from polyoxyalkylenetriamine and epoxideresin/amine adducts (b) 0 to 15 wt. % of an anti-corrosion pigment (c)40 to 70 wt. % of a conductive pigment selected from powdered zinc,aluminum, graphite, molybdenum sulfide, carbon black and iron phosphide(d) 0 to 45 wt. % of a solvent, and, if required, up to 50 wt. % ofother active or auxiliary substances, wherein the proportions of thecomponents total 100%
 2. A composition as claimed in claim 1 wherein atleast one epoxide based on bisphenol A glycidyl ether having a molecularweight of at least 800 is used as an epoxide resin.
 3. A composition asclaimed in one or both of claims 1 and 2, wherein it contains, ascomponent (b), at least one anti-corrosion pigment selected from dopedsilica, silicates of divalent metals, aluminum and zinc phosphates andmodification products thereof and surface modified titanium dioxide. 4.A composition as claimed in one or more of claims 1 to 3 whereincomponent (c) is iron phosphide.
 5. A composition as claimed in one ormore of claims 1 to 4 wherein solvent (d) is selected from diacetonealcohol, butyldiglycol acetate, aromatic-rich hydrocarbons, xylene,3-methyoxybutyl acetate, methoxyacetoxy propane, benzyl alcohol andbutanol.
 6. A composition as claimed in one or more of claims 1 to 5wherein it contains, as further active or auxiliary substances, one ormore substances selected from modified castor oil, modified polyethylenewaxes and polyethersiloxane copolymers.
 7. A composition as claimed inone or more of claims 1 to 6 wherein it does not contain isocyanates. 8.Use of the composition as claimed in any of the preceding claims forcoating metal strips in a coil-coating process.
 9. A process for coatingmetal surfaces with a conductive organic anti-corrosion layer,characterised by the following steps: (i) a conventional pretreatmentconsisting of cleansing phosphatising, if required chromatising, ifrequired chromium-free pretreatment, if required (ii) coating with acomposition as claimed in any one of claims 1 to 7, in a layer thicknessof 1 to 10 μm, preferably between 5 and 9 μm (iii) curing the organiccoating at temperatures between 160 and 260° C. peak metal temperature(PMT).
 10. A process as claimed in claim 9 wherein the metal surfacesare surfaces of aluminum or of galvanised or alloy galvanised steels.11. A metal object having an anti-corrosion layer which may be preparedby a process as claimed in one of claims 9 and
 10. 12. A metal objectwhich has a coating system on the metal surface consisting of thefollowing individual layers: (a) a chemical conversion layer, (b) aconductive organic layer having a thickness of 1 to 10 μm, containing atleast an organic binder and an electrically conductive substance, (c) apowder coating layer having a thickness of 70 to 120 μm.
 13. A metalobject which has, on the metal surface, a coating system consisting ofthe following individual layers: (a) a chemical conversion layer, (b) aconductive organic layer having a thickness of 1 to 10 μm, containing atleast an organic binder and an electrically conductive substance, (c) anelectrodeposition lacquer having a thickness of 25 to 35 μm (d) one ortwo layers of topcoat.
 14. A metal object as claimed in one of claims 12and 13 wherein the conductive organic layer (b) is obtainable by theprocess as claimed in one of claims 9 and
 10. 15. A metal object asclaimed in one of claims 12 and 13 wherein the conductive organic layer(b) is obtained by applying a coating agent having the composition: (i)10 to 30 wt. % of an organic binder which cures at a temperature of 140to 159° C., preferably between 149 and 159° C., (ii) 30 to 60 wt. % of apowder of an electrically conductive substance, (iii) 10 to 40 wt. % ofwater and (iv) if required, a total of up to 30 wt. % of other activeand/or auxiliary substances, wherein the amounts total 100 wt. %, to themetal surface provided with chemical conversion layer (a) and cured at apeak metal temperature in the range 130 to 159° C.
 16. A process forcoating a metal object, characterised in that the following layers areapplied in sequence to at least part of the surface of the metal object:(a) a chemical conversion layer, (b) a conductive organic layer having athickness of 1 to 10 μm, containing at least an organic binder and anelectrically conductive substance, (c) a powder coating layer having athickness of 70 to 120 μm.
 17. A process for coating a metal object,characterised in that the following layers are applied in sequence to atleast part of the surface of the metal object: (a) a chemical conversionlayer, (b) a conductive organic layer having a thickness of 1 to 10 μm,containing at least an organic binder and an electrically conductivesubstance, (c) an electrodeposition lacquer having a thickness of 25 to35 μm, (d) one or two layers of topcoat.